JPH06158114A - Cemented carbide mold for hot or warm forging - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a die made of cemented carbide for hot forging or warm forging having a long service life. [Structure] Co: 5 to 25%, C as a binder phase forming component
r: 0.3 to 3.0% (or more, weight%), and the balance consisting of WC of dispersed phase forming component and unavoidable impurities, and the above WC has an average particle size in the range of 1 to 5 μm. A cemented carbide die for hot or warm forging made of cemented carbide having a structure dispersed as fine particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a die made of cemented carbide which has a longer service life than ever before even when used for hot forging or warm forging.

[0002]

2. Description of the Related Art Generally, a die for cold forging precision small parts has a Co content of 5 to 25% as a binder phase forming component.
It is known that a cemented carbide containing (% represents% by weight, below,% represents% by weight) and the balance consisting of tungsten carbide (hereinafter referred to as WC) and inevitable impurities is used. .

[0003]

However, when the cold precision forging die made of the above-mentioned ordinary cemented carbide is used for hot or warm forging as it is, toughness is insufficient and cracking occurs,
There is a problem in that the hardness is insufficient, the wear progresses quickly, and the corrosion resistance and the oxidation resistance are poor, so that the skin becomes rough, and the life is reached after a relatively short period of use.

[0004]

Therefore, the present inventors have
From the above viewpoint, as a result of conducting research to develop a cemented carbide die that does not crack even if hot forging or warm forging is performed and is excellent in wear resistance and rough surface resistance. Cr as a binder phase forming component: 0.3 to 3% by weight,
The WC-based cemented carbide containing Co: 5 to 25 wt% has a hot forging temperature (above 1000 ° C.) and a warm forging temperature (200 to
It does not crack even under severe impact at 1000 ° C) and has excellent corrosion resistance and oxidation resistance, and hot or warm forging dies made of such WC-based cemented carbide are Therefore, we have obtained the knowledge that the service life will be further extended.

The present invention was made on the basis of such findings, and Co: 5 to 2 as a binder phase forming component.
5%, Cr: 0.3 to 3.0%, and a hot or warm forging die made of a cemented carbide having a composition consisting of WC as a dispersed phase forming component and unavoidable impurities. It has characteristics.

The WC of the dispersed phase forming component has an average particle size of 1
It is preferable that the fine particles are dispersed as fine particles within a range of ˜5 μm.

The reason why the constituent composition of the cemented carbide forming the hot or warm forging die of the present invention is limited as described above will be explained.

(A) Co The Co component has the function of binding the WC particles of the dispersed phase forming component to improve the toughness of the cemented carbide, but if the content is less than 5%, the desired toughness cannot be obtained. Its content is 25%
If it exceeds, the hardness is remarkably lowered and the wear resistance is lowered, so the content thereof is set to 5 to 25%.

(B) Cr The Cr component has the effect of forming a solid solution in Co, particularly suppressing the decrease in hardness at 200 ° C. or higher, and contributing to the improvement of corrosion resistance and oxidation resistance. If it is less than 0.3%, the desired effect cannot be obtained, while its content is 3.0%.
If it exceeds 0.1%, carbides will be precipitated in the binder phase and the toughness will be deteriorated, so the content thereof was set to 0.3 to 3.0%.

The reason why the WC as the dispersed phase forming component is limited to the average particle size of 1 to 5 μm is that the WC has an average particle size of 1
If it is less than μm, the desired toughness cannot be obtained, while the average grain size is 5
If the average particle size exceeds 1 μm, the wear resistance decreases and plastic deformation easily occurs, so the average particle size is 1 to 5 μm.
Limited to.

[0011]

【Example】

Example 1 As a raw material powder, Co having an average particle diameter of 1.2 μm
Powder and Cr powder were prepared, and further WC powder having the average particle size shown in Table 1 was prepared.

These raw material powders were blended to the blending composition shown in Table 1, mixed in a ball mill and molded into a green compact, and these green compacts were then heated in a vacuum of 0.07 Torr at a temperature of 1360 to 1430. Molds 1 to 5 of the present invention for hot forging an engine valve, which have a composition substantially the same as the composition and are sintered at a predetermined temperature in the range of ℃ for 1 hour. Molds 1 to 4 and a conventional mold 1 were produced.

These molds are filled with a forging material made of heat-resistant steel of SUH31 heated to a temperature of 1100 ° C., and an engine valve having a diameter of 30 mm is hot forged, so that the inner surface of the mold is roughened, worn or cracked. Until then, the number of engine valves manufactured by hot forging was measured, and the results are shown in Table 1.

[0014]

[Table 1]

From the results shown in Table 1, the molds of the present invention 1 to
It can be seen that in No. 3, as compared with the conventional mold 1, the number of engine valves manufactured by hot forging until the inner surface of the mold is roughened is remarkably large, and the life of the mold is long. However, comparative molds 1 or 2 having a composition or dispersed phase outside the present invention
It can also be seen that in No. 4, unfavorable phenomena such as easy cracking of the mold, rough skin and abrasion are likely to occur at an early stage, and the life of the mold is shortened.

Example 2 The raw material powder prepared in Example 1 was blended to the blending composition shown in Table 2, mixed in a ball mill and sintered under the same conditions as in Example 1 to obtain substantially the same blending composition. Molds 4 to 6 of the present invention for warm forging a constant velocity joint part having a composition,
Comparative dies 5 to 8 and conventional die 2 were produced.

A forging material made of ordinary carbon steel heated to a temperature of 900 ° C. was charged into these molds, and the diameter was 10
A 0 mm constant velocity joint member was warm forged, and the number of constant velocity joint members manufactured by warm forging was measured until wear or cracks on the inner surface of the die were measured, and the results are shown in Table 2.
It was shown to.

[0018]

[Table 2]

From the results shown in Table 2, the molds of the present invention 4 to
It can be seen that No. 6 has a longer service life than the comparative dies 5 to 8 and the conventional die 2 even when used for warm forging.

[0020]

When the die of the present invention is used for hot forging or warm forging, it has a much longer service life than before, and therefore the number of times of expensive die replacement is reduced and the cost is reduced. It is possible to achieve an excellent industrial effect. Further, it is needless to say that even if the die of the present invention is used for cold forging, the same or higher effect as the conventional die can be exhibited.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Itaro Tajima 1-297 Kitabukuro-cho, Omiya-shi, Saitama Prefecture Central Research Laboratory of Mitsubishi Material Co., Ltd. (72) Koji Shinohara 1-297 Kitabukuro-cho, Omiya-shi, Saitama Mitsubishi Materi Al Co., Ltd. Central Research Institute

Claims (2)

[Claims] 1. A composition containing 5 to 25% by weight of Co and 0.3 to 3.0% by weight of Cr as a binder phase forming component, and the balance comprising tungsten carbide as a dispersed phase forming component and unavoidable impurities. A die made of cemented carbide for hot or warm forging, characterized in that it is made of a cemented carbide. 2. The hot or warm forging according to claim 1, wherein the tungsten carbide as the dispersed phase forming component is dispersed as fine particles having an average particle size in the range of 1 to 5 μm. Carbide alloy mold for use.